In radio communication, particularly in the case of wideband transmission, there exist paths in addition to a path that arrives in advance, and these paths arrive delayed via reflection off obstacles such as buildings and mountains, for example. An environment in which multiple paths arrive in this way is called a multi-path environment. Recently, orthogonal frequency-division multiplexing (OFDM) is gaining attention as a technique of realizing reliable high-speed transmission in such a multi-path environment, and is being adopted in various fields, including next-generation mobile communication systems such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A), as well as wireless LAN and broadcasting. In the case in which a receiving device demodulates an OFDM signal, it is necessary to conduct channel estimation and compute the channel frequency response (CFR) for each subcarrier. There is a method of realizing this, in which a pilot symbol whose waveform (or alternatively, signal sequence) is stored in advance by the receiving device is transmitted from the transmitting device to the receiving device. Using this pilot symbol to conduct accurate channel estimation requires an accurate power delay profile (PDP).
PTL 1 describes a method of estimating channel impulse response. This method consists of a two-stage process of path extraction and channel impulse response estimation using the extracted path information. In the case of using this technology in OFDM, a time-to-frequency transform is applied to the estimated channel impulse response to convert to a frequency response before use.